1. Field of the Invention
The present invention relates to an autofocus distance-measuring optical system, equipped with an autofocus system, which can be incorporated in an electronic distance meter, wherein the distance-measuring optical system has a function to measure the distance between two points and also a function to focus a sighting telescope on a sighting object automatically via the autofocus system.
2. Description of the Related Art
A conventional surveying instrument such as a total station has a function to measure the distance between two points and also horizontal and vertical angles. Such a conventional surveying instrument generally measures the distance between two points with an electronic distance meter (EDM) incorporated in or attached to the surveying instrument. The electronic distance meter incorporates an optical distance meter which calculates the distance from the phase-difference or the time difference between the measuring light (externally-projecting light), which is projected toward a target, and the internal reference light.
On the other hand, advancements have been made in the development of surveying instruments provided with a sighting telescope (collimating telescope) having an autofocus system, wherein phase-difference detection type autofocus system is widely used in the autofocus therefor. With this system, an in-focus state is detected based on the correlation between two images formed by two light bundles which are respectively passed through two different pupil areas upon passing through different portions of an objective lens of the sighting telescope to bring the sighting telescope into focus in accordance with the detected in-focus state.
However, if a phase-difference detection type autofocus system is simply incorporated in the electronic distance meter (provided in a surveying instrument), one or more components of the optical distance meter of the electronic distance meter interfere with the two different pupil areas of the phase-difference detection type autofocus system. In other words, the bundle of rays that pass through the two different pupil areas, and pass through different portions of an objective lens of the sighting telescope, interfere with components of the optical distance meter of the electronic distance meter, which deteriorates the precision in focus detection, and thus deteriorates the performance of the autofocus system.
The present invention has been devised in view of the problems noted above, and accordingly, an object of the present invention is to provide an autofocus distance-measuring optical system, equipped with an autofocus system, which can be incorporated in an electronic distance meter, wherein the optical distance meter thereof does not deteriorate the performance of the autofocus system.
To achieve the object mentioned above, an autofocus distance-measuring optical system is provided, including a sighting telescope having an objective lens for sighting an object; an optical distance meter which includes a light-transmitting optical system for transmitting a measuring light via the objective lens, and a light-receiving optical system for receiving light reflected by the object; a focus detecting device for detecting a focus state of the sighting telescope; and a controller for controlling the sighting telescope to automatically focus on the object in accordance with the focus state detected by the focus detecting device. The focus detecting device includes a phase-difference detection type of focus detecting device which detects an in-focus state from a pair of images respectively formed by two light bundles which are respectively passed through two different pupil areas of the phase-difference detection type of focus detecting device and passed through different portions of the objective lens of the sighting telescope. The two different pupil areas are positioned so that the two light bundles which pass therethrough do not interfere with any optical elements of the optical distance meter.
Preferably, at least one lens element of the objective lens is utilized as a focusing lens group which is moved in accordance with the focus state detected by the focus detecting device.
In an embodiment, the sighting telescope includes an optical system positioned between the objective lens and the focus detecting device, wherein the optical system functions so that the combined focal length of the objective lens and the optical system is longer than the focal length of the objective lens.
In an embodiment, the optical system includes a focus adjustment lens having a negative power, the focus adjustment lens being moved in accordance with the focus state detected by the focus detecting device.
Preferably, the light-transmitting optical system includes a reflection member positioned on an optical axis of the objective lens, wherein the two different pupil areas are positioned so as not to interfere with the reflection member.
Preferably, the optical elements of the optical distance meter are arranged in a direction defined along a line which extends across the diameter of the objective lens and passes through the optical axis of the objective lens. Each of the pupil areas is determined so as to have an elongated shape extending parallel to the above-mentioned direction, so as not to interfere with the optical elements arranged in the direction.
Preferably, the focus detecting device includes a pair of line sensors on which the pair of images are respectively formed by the two light bundles.
Preferably, the focus detecting device includes an AF sensor unit in which the pair of line sensors is accommodated.
According to another aspect of the present invention, an electronic distance meter is provided, including a sighting telescope; an optical distance meter; an AF sensor unit which detects a focus state of the sighting telescope; and a controller for driving an objective lens of the sighting telescope to focus the sighting telescope on a sighting object in accordance with the focus state detected by the focus detecting device. The AF sensor unit includes a phase-difference detection type AF sensor unit which detects an in-focus state from a pair of images respectively formed by two light bundles which are respectively passed through two different pupil areas of the phase-detection type AF sensor unit and passed through different portions of the objective lens of the sighting telescope; wherein optical elements of the optical distance meter are positioned so as not to interfere with the two different pupil areas.
According to another aspect of the present invention, an electronic distance meter is provided, including a sighting telescope including an objective lens and an eyepiece; an optical distance meter; a phase-difference detection type of AF sensor unit which detects an in-focus position from a pair of images respectively formed by two light bundles which are respectively passed through two different pupil areas of said phase-difference detection type of AF sensor unit and passed through different portions of the objective lens; a focus adjustment lens positioned between the objective lens and the eyepiece to extend a focal length of the objective lens; and a controller for driving the focus adjustment lens to focus the sighting telescope on a sighting object in accordance with the in-focus position detected by the focus detecting device; wherein optical elements of the optical distance meter are positioned so as not to interfere with the two different pupil areas.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-066230 (filed on Mar. 10, 2000) which is expressly incorporated herein by reference in its entirety.